OL 11 Flashcards
(26 cards)
what does the beam splitter do in the Michelson interferometer?
splits light into 2 beams
what is the property of the two beams after the beam splitter does its job?
both beams have the same amplitude, frequency and wavelength.
whats the difference in the beams produced by the beam splitter?
path length (distance the beam travels from the source to the detector)
what are the measurements in the Michelson interferometer based on?
- the appearance of the interference pattern
- the number of times the interference pattern changes from constructive to destructive interference when adjusting the mirror.
when two light beams in the michelson interferometer are brought together, what is the resultant amplitude dependant on?
the resultant amplitude is dependant on the phase difference (phase shift) between the 2 beams
in the Michelson interferometer a _______ beam of light is split into ____ these beams travel a certain ________ before each is being brought back together. The ______ _____. -_______ depends on the ____ difference between the ____ beams and builds the basis of _____/______ measurements
coherent 2 distances resultant light intensity path 2 length / depth
what part of the Michelson interferometer is able to move? and effects of this?
the mirror
is able to move back and forth,
the combined light beams are able to move in and out of phase as
the phase shift varies continuously
how long is phase of light in- interference in ophthalmic imaging- predictable and unpredictable?
phase of light is predictable for a finite length of time
phase of light is unpredictable for longer periods of time
in ophthalmic imaging, interference is produced using what kind of light source?
low coherence light sources
what is the coherence length calculation?
L= (wavelength)^2 divided by n (triangle wavelength)
n= refractive index of medium
wavelength squared= is the central wavelength of the source
triangle wavelength= spectral width of source
what are the advantages of low coherent light sources?
- creation of a fringe pattern which is useful to assess structures
- less powerful light source with respect to intensity and possible harm to ocular structures
what does low coherence imply?
implies that is not a single wavelength but a range of wavelengths but not from a whole spectrum
what does the spacing of the fringe pattern provide?
gives position of the tissue layers in depth
what happens when you move the reference mirror back and forth in ophthalmic imaging
3 interference fringe patterns will be created
what kind of light source is used in OCT?
near infrared
most tissues are partially transparent to what in ophthalmic imaging/ OCT?
most tissues are partially transparent to near infrared light
what happens to the light in OCT? what does this enable?
some light is scattered back to the detector but some will be transmitted to deeper layers before it is reflected
-this transmission allows us to get a depth profile of the tissues assessed
what is the wavelength is long in ophthalmic imaging, what des it enable?
longer the wavelength the greater the tissue penetration
describe the mirror used in time domain OCT system?
moveable mirror
describe the light source used in time domain OCT system?
low coherence near infrared light
produced using a superluminescent diode
what happens to the measurement beam in time domain oct system?
the measurement beam is reflected or back scattered from the object ( e.g retina)
with different delay times (which are dependant on the optical properties of the ocular tissue)
how is the axial profile of reflectivity versus depth obtained in Time domain OCT?
by movement of the reference mirror
which changes the path length in the reference arm
how can the depth of the tissue be determined in Time domain OCT?
for each point on the retina,
magnitude of intensity of resulting interference fringes,
is recorded for each position of reference mirror and computer processing…. which determines the depth of tissue.
what is the axial and transverse resolution of time domain OCT?
Axial = 10-15 microns transverse= 15 microns
